Present internal combustion engines are being manufactured for increased efficiency and greater horsepower outputs. In order to achieve greater efficiency, exhaust temperatures are increased as less heat is transferred to the cooling system. The increased exhaust temperatures increase the output of any exhaust energy recovery hardware, such as the turbocharger, and subsequently, the performance of the engine. Typically, current engine valve guides are made from an iron base material which operate within a limited maximum temperature range. Consequently, the iron base valve guides are not conducive for operating within the high exhaust temperature ranges reached with high efficiency engines. In order to utilize a valve guide within high exhaust temperatures, alternative materials must be used. One proposed solution to the above problem is to use a ceramic material for the valve guide. Ceramics typically have much higher temperature capabilities than the current iron based material. However, the use of ceramic materials for the valve guide is complicated by their typically low coefficient of expansion. If the valve guide material is merely changed from the current iron based material to a ceramic and it is installed in the conventional manner, such as shrink-fitting into the cylinder head, the resulting interference fit will disappear when the engine is brought up to operating temperature. This is due to the differential thermal expansion between the ceramic and the cylinder head material, typically cast iron or aluminum.
An example of a valve guide composed of a ceramic material is disclosed in U.S. Pat. No. 4,688,527 issued to Donald H. Mott et al. on Aug. 25, 1987. This prior art design for inclusion with a cast metal cylinder head includes a ceramic valve seating and stem supporting integral device for supporting and sealingly interacting with a conventional engine poppet-type valve. The device is integrally cast together to form a unit for subsequent inclusion within the metal cylinder head of the internal combustion engine by casting. However, casting ceramic components within a cylinder head can be an expensive endeavor. The shrinking of the cast metal during the casting cooling process has a strong potential for over stressing the ceramic insert and causing it to crack. Exotic, precise, and costly controls must be maintained during the casting process to avoid this concern. The resultant interference fit, achieved during the casting cooling, will be lost once the engine is at operating temperature due to the differential thermal expansion between the ceramic and the cylinder head material. Additionally, such a cast-in ceramic insert does not allow the replacement of either the valve guide or the valve seat. This renders the cylinder head unsuitable for rebuilding in the event of either a component failure or time related wear-out.
The present invention is directed to overcoming the problems as set forth above.